Glass or plastic is usually used as the transparent material for picture display screens such as CRT, LCD, and show window screens. However, because glass and plastic are insulating materials, their surface resistance is very high, and, therefore, electrostatic charges are liable to be accumulated thereon. If such electrostatic charges are accumulated, foreign material such as dust from the external air adheres to the surface of the screen. As a result, the screen is contaminated, the resolution of the displayed picture is lowered, and a person who touches the screen may experience an electric shock. In particular, if electrostatic charges are accumulated on the base plate of an LCD, false operations may occur in such a form that a segment is driven at a location where a driving voltage is not applied. Recently, in CRTs used as computer monitors, a user's likelihood of contacting the screen has become more frequent with the adoption of the screen contact data input system, for example. Accordingly, the problems of false operations and electric shock have become more serious.
Furthermore, when a flat glass or plastic panel is used as a screen, the surface of the screen reflects the ambient light in the normal direction, and, as a result, the picture on the screen becomes unrecognizable. This phenomenon becomes proportionately more severe with increased intensity of the ambient light, and therefore, the low luminance display devices such as LCD and the like produce a less clear or recognizable picture when the display device is operated with high luminance. Furthermore, CRTs used in televisions and monitors produce unclear pictures in such cases, and therefore, if they are watched for a long time, the eyes of the user become tired. Because of these problems, there is a need for eliminating or reducing glare on the surface of the picture display screen.
Under such a circumstance, various proposals have been made in order to reduce the glare of the screen.
For example, there has been proposed a method of forming a rough surface on a screen using a mechanical grinding process, or a selective etching process employing fluoric acid and the like. However, these methods are disadvantageous in that contamination and damage to the screens can occur during processing to an extent that regeneration of the screens is not possible. Further, the transparency of the screen can deteriorate due to the attraction of dust, which lowers the resolution of the picture.
Another proposal is to spread a plastic film or aqueous alkali silicate solution (the so-called water glass) on the surface of the screen. However, this is disadvantageous in that damage to the coating is likely to occur, and the organic solvent or the alkaline substance is likely to be eluted, thereby causing white opaqueness and deterioration in the resolution of the screen.
Still another proposal is to deposit a layer of conductive metal on the surface of the screen using a vapor deposition or sputtering method so that the antistatic and non-glare characteristics are provided simultaneously. However, this is disadvantageous in that the strength of the coating layer is weak, its durability is poor and a very large complicated deposition apparatus is needed. Therefore, it would be impractical in an industrial application.
Japanese Patent Laid-open No. 86-118932 discloses a method in which an alcohol solution of alkyl silicate having the chemical formula Si(OR).sub.4, where R is an alkyl group, is spread and polycondensated to that a SiO.sub.2 coating having tiny pockmarks is formed. According to this method, not only non-glare but also antistatic characteristics can be obtained by grounding the coating, because the silanol group (.tbd.Si--OH) reacts with the moisture of the atmosphere and, as a result, has conductibility.
However, according to the method of Japanese Patent Laid-open No. 86-118932, high temperature baking at 200.degree. C. or more has to be carried out to obtain a sufficient coating strength. Furthermore, this method cannot be used with a transparent material such as plastic, and sufficient conductivity cannot be obtained because the silanol base is polycondensated during the baking process.
In order to overcome the above-mentioned problems, Japanese Patent Laid-open No. 86-118946 discloses a method in which an alcohol solution of alkyl silicate is spread and is baked at a low temperature. However, in this method, as well as the methods mentioned above, ionic conduction which is obtained depends on the moisture of the external air, and therefore they cannot provide sufficient antistatic qualities in a dry region or in a dry season. Further, since the initial coating strength is very unstable, damage is likely to occur and degradation occurs with the lapse of time.
Japanese Patent Laid-open No. 86-16452 discloses a method in which an inorganic metal compound is put into silicate in order to improve conductivity. In this case, if the coating layer does not contain a conductive compound such as SiO.sub.2, the electric resistance of the coating layer cannot be reduced. Further, the coating layer which contains an absorptive inorganic metallic compound such as PdCl.sub.2 reduces its surface resistance by utilizing the absorbing property so that an antistatic property is obtained. If the humidity of the external air is not high enough, the antistatic effect cannot be obtained. The durability of the coating layer, particularly in terms of moisture resistance and chemical resistance, is very weak.
Japanese Patent Publication Laid-open No. 88-131408 discloses a composition in which the conductive oxide particles are dispersed and used in a matrix with the zirconia obtained from a zirconium salt. However, this requires complicated processes such as hydrolysis, filtering, cleaning, baking, crushing, dealkalinizing and the like in order to form the particles of the conductive oxide. Further, in preparing the composition, a crushing device and a dispersing device for uniformly distributing the ingredients are needed, as well as an additive such as a growth retardant. The resultant coated layer is porous, and therefore the transparency of the screen is lowered.